It is known that environmental factors, such as smoking, radiation, chronic inflammation caused by virus infection, etc, and exposure to toxic chemical substances influences to onset and development of cancer. Previous researches have revealed that oxidative stress caused by factors which causes abnormalities of DNA and protein is with the development of cancer.
A living organism has the physiological defense mechanism against such oxidative stress. A transcription factor called Nuclear factor erythroid 2-related factor 2 (NRF2) is recognized as one of the important molecules that plays a role in molecular mechanism of said physiological defense system. NRF2 is a DNA binding molecule with high transcriptional induction ability, which is activated when a cell is exposed to oxidative stress, and induces the expression of many groups of enzymes, such as glutathione reductase, which relieve oxidative stress, to protect a cell from the disorder caused by the stress.
For example, NRF2 is known as an important transcription factor that transmits a promoting signal to an antioxidant response element (ARE) component, which is a DNA regulatory element controlling transcription of the gene products which protect cells from carcinogens, oxidants, and other toxic compounds. It has been reported that an enhancer via ARE having cancer inhibitory activity increases the NRF2 level in the nucleus (see Yuesheng et al. Molecular Cancer Therapeutics, 3 (7) 885-893, 2004). In the oral administration model of the benzo-alfa-pyran, it has been appeared that the number of cancers are increased in NRF2 knockout mice compared to in wild type (see Ramos-Gomez et al. Proc. Natl. Acad. Sci. USA, 98, 3410-3415, 2001). In addition, the document suggests that an anticancer agent oltipraz increases the expression of NRF2, and that the anticancer effect of oltipraz is not seen in NRF2 knockout mice, and thus enhancement of NRF2 expression may lead to the anticancer effect.
Furthermore, it has been reported that in a living organism an existence of NRF2 is controlled by negative feedback of Kelch-like ECH-associated protein 1 (KEAP1), and an inhibitor to KEAP1 is under development as an anticancer agent (see Ewan, Drug Discovery Today, 10 (14) 950-951, 2005). Thus, it is expected that drugs targeting NRF2 or KEAP1 which enhance the expression of NRF2 may be used as an anticancer agent.
On the other hand, it is reported that, in lung cancer, constant activation of NRF2 is observed due to the reduced activity of KEAP1 caused by KEAP1 gene mutation is observed and that the activated NRF2, induced constant expression of an anti-oxidant protein. It has been reported that increased expression of NRF2 may be one of the reasons of the resistance of a cancer cells to cisplatin (see Ohta et al. Cancer Res., 68, 1303-1309, 2008 and International Publication WO2006/128041). It has also been reported that administration of alkylating agents such as cisplatin, mephalan, chlorambucil, and BCNU increases the expression of a gene regulated by ARE, such as NRF2. It has been suggested that the increased gene expression products regulated by ARE can be involved in the resistance of cancer cells to the anticancer agents. It has also been suggested that all trans retinoic acid (ATRA), which can bind to NRF2, may be able to enhance the effect of a chemotherapic drug (see International Publication WO2008/012534).
Thus, it is appeared that administration of an alkylating anticancer agent may activate NRF2, and the NRF2 may play a role in resistance to the alkylating anticancer agent. An alkylating anticancer agent interrupts proliferation by cross-linking bases of DNA in a cancer cell. The mechanism of activation of NRF2 upon administration of an alkylating agent remains to be explained. Although a part of mechanism of the acquisition of resistance due to NRF2 against the effect of an alkylating anticancer drug is predicted from a cytoprotective action of NRF2, the overview is not fully understood yet. The relation between anticancer agents other than an alkylating anticancer agent and NRF2 has not been reported.
As noted above, activation of NRF2 observed in a cancer cell has been considered mainly based on the reduced activity of KEAP1 due to KEAP1 gene mutation. The relation between mutation and activation of NRF2 in a cancer cell, and the relation between the NRF2 activation due to the mutation and the malignant alteration of cancer have not been known. Especially, NRF2 has been thought to have an anticancer effect in the onset of the cancer caused by oxidative stress, etc. it has been considered that NRF2 rather suppresses the malignant alteration of cancer. In relation with a chemotherapic drug, it has suggested that NRF2 is responsive to administration of an alkylating agent, and, at least, an all trans retinoic acid enhances the effect of an alkylating agent. However, it has been completely unknown whether an effect of an all trans retinoic acid is based on NRF2 suppressing effect, and if so, what mechanism underlies inhibition. Therefore, the relation between suppression of NRF2 and anticancer agents other than an alkylating anticancer agent has been wholly unknown.
Mammalian target of rapamycin (mTOR) is a serine threonine kinase identified as a target molecule of a macrolide antibiotic, rapamycin and it serves as regulator on cell growth, cell proliferation, cell motility, cell survival, protein synthesis and transcription. Since a rapamycin induces an apoptosis of a cancer cell lacking the function of p53, it is considered that an mTOR inhibitor has an anticancer activity (see Shile Huang et al. Molecular Cell, 11, 1491-1501, 2003). In addition, mTOR inhibitors have been under development as anticancer agent for, for example, renal cancer and pancreatic duct cancer.
An mTOR is also known as an insulin receptor tyrosine kinase. A research on the apoptosis of cerebrovascular endothelial cells in a hyperglycemia patient concludes that an mTOR inhibitor impairs expression of insulin-inducible NRF2-mediated Glutamate-L-cystein ligase-catalytic subunit (GCLc), oxidation reduction balance, and survival of a human cerebrovascular endothelial cell (see Okouchi, Masahiro et al. Current Neurovascular Research, 3 (4) 249-261, 2006). However, especially as for the field of cancer treatment, the effect of the expression of NRF2 on an action of an mTOR inhibitor has not been reported yet.